Gating modulation



Oct. 6, 1 959 GATING MoDuLATIoN Filed Nov. 15, 1957 ATTORNEYS United States Patent O 2,907,956 GATING MoDULATIoN R Lee Hollingsworth, West Hempstead, NY.

Application November 15, 1957, Serial No. 696,801

6 Claims. (Cl. 332-41) 'Ihe present invention relates to a system for applying a modulating signal to a carrier frequency iny such a Way that high percentage modulation may be obtained. The present invention provides a novel gating system to greatly expand a limited value of carrier power.

Heretofore it has been known to apply a modulating signal to one, or more than one tube` in a carrier frequency channel, but not in such a manner as to get high percentage modulation, such as herein attained.

It is an object of my invention to provide a circuit in which a modulating signal is applied through a gating circuit comprising preferably two tubes, preferably triodes connected in parallel With their grids separately and differently biased and the two tubes receiving respectively modulating signal of different amplitude.

It is `another object of my invention to provide a circuit in rwhich modulating signal is preferably applied separately to the anodes of two or more carrier-frequency tubes connected in series or cascade.

It is another object to provide a modulated transmitter of high eliiciency.

It is still another object of the present invention to provide a method of transmission with minimum carrier transmission when zero modulation is applied.

My invention Will be understood by reference to the following specication together with the accompanying drawing, wherein the ligure shows a circuit embodying my invention.

In the drawing, T1 and T2 are a pair of dissimilar triodes having cathodes and anodes connected in parallel, T2 being capable of rather high current, equal to the total of tubes T3 and T4, While T1 may be considerably smaller having a current carrying capacity sulcientto maintain the plate `currents from triodes T3 and T4 at the value to cause for example 100 watts of canrier energy to be supplied to the antenna, as triode T2 goes: through the negative portion of the cycle of modulation, which might on bursts or peaks, reduce its current to zero. The modulating signal voltage is applied at the input connections 1 of primary 4 ofytransforrner 5. One terminal of one secondary'winding 6 oftransformer 5 is connected to the negative terminal of grid bias battery 14 and to the cathode 10 of tube T2, While the other terminal of Winding `6 is connected to the grid 36 of T2. Another secondary winding 7 of transformer 5 is shunt'ed by a variable resistance 7-a (to give a loss of 32 decibels approximately), one side of Winding 7 being connected to the negative terminal of bias battery 13, while the other side of the secondary Winding 7 is connected to grid 35 of triode T1. Cathodes 9 and 10 are connected together and to the plates of T3 and T4 through iilters 31-32 and 33-34 respectively. Plate 11 of triode T2 is connected directly to the plate supply source 12, While plate 8 of triode T1 is connected to the same plate source 12, through a voltage'dropping resistor S-a.'

T3 is 'an amplilier-modulator triode having cathode 15, grid 16, and anode 17. Itsinput circuit including 2,907,956 Patented Oct. 6, 1959 its grid 16 and 4cathode 15 is inductively coupled through transformer 19 to a source 18 of carrier frequency potential. Cathode resistor 24 is in series with cathode 15 and is grounded. The output circuitbetween anode 17 and cathode 15 of-triodeTS is inductively-,coupled Vto the input circuit of an amplilier-modulator tube T4 in cluding its grid 22 and cathode 21 through transformer 2li. CathodeZl of triode T4 is connected through cathode resistor 25to ground.

The output"cireuit oftriode T4 between anode 23 and cathode.21 -is inductively coupled to the antenna circuit 28 through transformer 26 whose secondary `shunted by condenser 27. '5A lilter 29 connected be?? tween the antenna circuit and groundv removesV carrier harmonics and prevents this harmonic energy from ybeing radiated by the antenna v28.

Although tubes T3'and T4 :are shown to be selffbiased,

it is to be appreciated that they'may have a separate-i grounded condenser' Y34'.V

Inserted in this connection from the cathode's bf T1` and T2 is also a variable resistor R, which is adjusted to control the output of triode T3 looking into control grid 22 of tube T4. T3 and T4 are driven so that a peak modulated wave of say 4000 watts is transmitted at a given modulation referencer level that can vbe said to be When no modulating signal is applied from signal source 1, the gating circuit including triodes. T1 and T2 -is almost completely blocked by biasing batteries 13 and 14. With no modulating signal applied, triodes T3 and T4 pass toward the antenna a relatively weak canrier signal such as 100 Watts for example, which is rich in harmonics. Under these conditions both of triodes T3 and T4 act vsubstantially as limiters due to the low anode voltage which is applied to them.

When a modulating signal is applied from signal source 1, the gating circuit including triodes T1 and T2 conducts the signal to the anodes of triodes T3 and T4, by reducing the pure resistive value of T1 and T2. 'The modulating signal applied at input 1, may be compressed or automatically controlled as desired, 1depending largely upon the characteristics of T1 and T2. This allows triodes T3 and T4 to amplify in a normal manner to give a peak output from triode T4 of say 4000 watts.

Since the output of triode T3 is to be amplified in triode T4, it is desirable to adjust the setting of variable resistance R to a value which 'will give the desired carrier drive to T4. For instance, resistance R is adjusted so that with full modulation, the radio frequency peaks of the output of triode T4 will rise to a desired value such as 4000 watts, With the additive amplification of triodes T3 and T4, With 100% reference modulation applied.

With this arrangement, a high degree of modulation is obtained in the madulated output of triode T4 which is applied to the antenna. It is to be realized that with an applied modulating signal, as T2 cuts olf completely on the negative portion of the modulation cycle, the grid lvoltage of T1 is increasing to cause T1 to draw current sucient to keep at least 100 watts of power flowing into the antenna.

It is to be also appreciated that T1 and T2 can modulate one or more tubes as desired. It is to be noted that the modulating circuit will operate Well with only T2 if positive control is applied by a limiter or the like to insure that the required minimum plate current is passed from the amplier tubes through the modulating device.

For lower quality transmission' however no carrier, or substantially no carrier, need be transmitted when no modulation is applied.

What I claim is:

1. In a modulating system, a source of modulating signal, a gating circuit comprising a pair of gating triodes having their cathodes and anodes connected in parallel, separate transformer means for applying said modulating signal to the respective grids of said gating triodes, separate biasing means for normally biasing the grids of said gating triodes respectively with biasing voltages of difterent magnitudes, a lirst amplier-modulator triode and a second amplier-modulator triode, a source of carrier frequency current coupled to the input circuit of said rst amplifier-modulator triode, the output circuit of said rst amplifier-modulator triode between its anode and cathode being coupled to the input circuit of said second amplifier-modulator triode, an output circuit for said second amplier-modulator triode connected between its anode and cathode, a first signal feed circuit between the parallel connected cathodes of said gating-triodes and the anode of said first amplifier-modulator triode, and a second signal feed circuit between the parallel connected cathodes of said gating triodes and the anode of said secondl ampliler-modulator triode.

2. A modulation system according to claim 1, and a variable resistance connected in series in said lirst signal feed circuit.

3. A modulation system in accordance with claim 1, wherein differential modulation voltages derived from said source of modulating signal through said biasing means are applied to the grids of said gating triodes.

4. A modulation system in accordance with claim l and means for supplying anode voltages of different magnitudes to the anodes of said ltwo gating triodes.

5. A modulating system according to claim l, a source of anode potential for said gating triodes, the anode of a rst one of said gating triodes being connected to said source of anode potential, and a voltage dropping resistor connected in series between the anode of the second one of said gating triodes and said source of anode potential.

6. In combination, the `invention recited in claim 1, wherein the carrier frequency amplifiers are operated as limiters with no modulation applied, said carrier frequency ampliers changing in characteristics from limiting to class C, and through class C ampli'lication returning progressively back to limiting with each full power reference level cycle of applied modulation, the nal of said carrier frequencyV amplifiers connected to an antenna through a harmonic lter.

References Cited in the tile of this patent UNITED STATES PATENTS 2,038,526 Ditcham Apr. 28, 1936 2,235,549 Dome Mar. 18, 1941 2,436,066 Favre Feb. 17, 1948 2,463,275 Henderson Mar. l, 1949 l l l 

